(a) Field of the Invention
The present invention relates to optical sensor means for image recognition, in particular to a photocoupler for use in optical detection of printed pattern of a bill which passes through a currency validator.
(b) Description of the Prior Art
An apparatus for currency validation is equipped in a bill handling machine such as currency exchanging or vending machine installed indoor or outdoor. The machine comprises a validator for identifying authenticity of bills inserted therein and a stacker for storing accumulated bills considered authentic by the validator. In most of the bill handling machines, the validator is mounted in driving connection to the stacker and secured to an inner surface of a door panel of the machines so that bills may be received by the validator through an inlet formed in a fixing panel of the machine. Equipped with the validator is a belt-pulley arrangement for transporting the inserted bill through a position in the vicinity of a sensor to the stacker. The sensor comprises optical or magnetic detector which converts physical features of the bill into electric signals then forwarded to a central processing unit.
Prior art optical sensors comprise a photocoupler for image recognition which includes a light emitting diode and a light sensitive transistor to detect printed white and black pattern of the bill. Light emitted from the diode is formed into a round light image on a surface of the bill and then is reflected on the surface of the bill and received by the transistor which detects the round light image. Whereas the pattern of the bill includes printed fine dots or lines, the transistor only detects the reflected round light image and therefore can not clearly detect fine dots or lines of the pattern.